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NBME 23 Answers

nbme23/Block 1/Question#33

A 25-year-old woman and her 25-year-old husband ...

α-Thalassemia trait

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I found a picture showing the transmission by two heterozygous alpha thalassemia trait asian (cis-deletion) parents, and modified it to also show the inheritance by two heterozygous alpha thalassemia african (trans-deletion) parents. Here you go: https://drive.google.com/open?id=1HQU1VuhI4Jc9WJR2POwnTq9T8wEdv7dw

 +4  upvote downvote
submitted by asapdoc(20),

Dr.Goljan explains it really well on the audio. I will just give the basic idea. All the hemoglobins have alpha in it therefore you cannot notice it on hemoglobin electrophoresis

someduck3  Just to add to this; a-thal is due to a deletion. While b-thal is due to a mutation. If they had a b-thal there would be target cells. a-thal just presents as microcytic & hypochromic. +2  

bc the parents are asian, they are cis deletion carriers. So their kid can either be a cis carrier or have Hb Barts, its not possible to get HbH

In what situations will HbH be formed (3 alpha chain deletions)?

 +0  upvote downvote
submitted by nor16(10),

in ß Thalassemia there is HbA2 increase and HbA decreases, even in ß+ , normal electrophoresis rules this out. same for A)-C)